There have been many changes in the human living environment and living means due to economic development following industrialization, and increased indoor dwelling time due to development of information communication technology has led to a new environmental problem of indoor air contamination.
When contaminated air is generated in limited space such as the indoors, concentration of the contaminated air increases over time due to circulation of the contaminated materials, thereby an individual may be exposed to microbiological harmful factors such as infectious bacteria and mold including various dust, and this may result in body fatigue, malaise, headache, and infectious diseases and hypersensitivity diseases in the respiratory system and the integumentary system.
In addition, such contamination of indoor air can increase risk of infection for patients in immunocompromised state and elderly patients. Further, research results have shown that intake of various harmful materials due to contamination of indoor air quality, work-related stress and blood flow disorders cause negative effect by increasing the numerical value of reactive oxygen species (ROS) within the body of patients and indoor residents.
The increase in reactive oxygen species as stated above is generated through various metabolic processes when oxygen absorbed into the body during respiration is used in oxidation processes of the body. The oxygen attacks biological tissues to destroy lipids, proteins, and nucleic acids (DNA, RNA), inhibits enzyme function, and promotes a variety of diseases (cancer, aging, etc.), but this also affects neurotransmitters DOPAMINE SEROTOMIN and ACETYL-CHOLINE, as well as ACETYL-CHOLINE ESTERASE, thereby significantly decreasing the immune function.
Meanwhile, research has actually been underway since 1980 based on research results in which nitric oxide (NO) was found to promote health of the cardiovascular system through vasodilation and the antioxidative activity (SOD) which reduces levels of reactive oxygen species in the body.
In particular, the study on nitric oxide as above is derived from the discovery of endothelium-derived relaxing factor (EDRF), and there have been reports of unknown strong blood vessel relaxing factor being produced in the endothelial cells of the blood vessels (EDRF), with the EDRF being identified as nitric oxide (NO).
Nitric oxide (NO) is produced together with L-citrulline by nitrogen monoxide (NO) generating element (NITRIC-OXIDE SYNTHASE; NOS) in L-arginine, and research results have been reported where in regards to the nitric oxide activity in the body, nitric oxide was produced in the vascular endothelial cells to activate guanylate cyclase of the vascular smooth muscle and cyclic GMP were produced to relax the blood vessels. As this study progressed, various other functions of nitric acid (NO) were discovered one after the other in addition to nitric acid (NO) being a signaling molecule playing a key role in the cardiovascular system.
In addition, nitric oxide (NO) is currently known to perform various functions such as blood flow regulator of various body organs, blood pressure regulator, and neurotransmitter in the nervous system fighting infections. Further, the in-depth study by Robert F. Furchgott, phD, Louis Ignarro, phD and Ferid Murad, phD on how the nitric oxide (NO) exists in almost all organisms and is produced by a variety of different types of cells was recognized for its achievement in 1998, thereby the above three researchers were awarded the Nobel Prize in Physiology or Medicine by the Nobel Committee at the Karolinska Institutet in recognition of their merit on “discovering nitrogen monoxide (NO: NITRIC OXIDE) as the signaling molecule in the cardiovascular system”.
However, the endothelial cells by itself cannot produce enough nitric acid required for physiological functions in the body due to various factors such as contamination of indoor air quality, nutritional deficiencies in the diet, lack of exercise, overwork and drug intake. Thus, the nitric acid must be directly or indirectly supplied from outside through various means.
As an example, there exist a method of producing nitric acid for producing nitric oxide (NO), that is, nitrogen monoxide is produced in the process of oxidizing ammonia with oxygen and carrying out absorption in water. However, this method could not be practically used due to the ammonia material being harmful to the body, increased malodor concentration and having fire risk.
In response to the above, the Korean Patent No. 10-0203721 (Method and Apparatus for Production of Nitric Oxide Gas Mixture) introduced a method of placing feed gas containing oxygen and nitrogen, oxygen and ammonia, and oxygen and ammonia nitrogen to a Group VIII catalyst within a temperature range of about 300˜1200 degrees Celsius in order to produce a mixture containing nitrogen dioxide. However, this method requires a separate heating apparatus for raising the gas temperature to 300˜1200 degrees Celsius resulting in excessive energy cost, and the ammonia gas used in the process affects the respiratory system. Also, inherent fire risk exists which requires separate safety measures.
In addition, the Korean Patent No. 10-0978805 (Refining Method and Equipment of High Purity Nitric Oxide using Cryogenic Freezing Trap) introduced a method in which low-temperature cooling was performed on nitrogen monoxide gas flowing in from the low purity nitrogen monoxide feed tank, which was then passed through an absorbent to remove impurities, and afterwards underwent phase change at low temperature to carry out secondary removal of impurities, and refined nitrogen monoxide at very high vacuum. However, this method requires a separate low purity nitrogen monoxide feed apparatus, the apparatus is complex due to components such as cryogenic freezing system and reaction tank, and has high energy consumption.
Thus, nitric oxide generator developed until now have selectively used ammonia which is a toxic and combustible material harmful to the body, required a separate heating apparatus for raising the gas temperature to a range of 300˜1200 degrees Celsius, had increased operating and maintenance costs due to high energy consumption, had high initial investment costs since separate nitric oxide feed apparatus and cryogenic freezing system were required, and the large size of the apparatus limited the apparatus from being purchased for use at homes or business facilities.